When I write tests and I exactly know what I need I write a test first. Other times I experiment with the implementation and then write some tests after the code exists. And for some code the effort to write a automated tests is not worth it.

However, there is one advice I need to remind myself from time to time: Write a failing test first. Or, when you write the test afterward, make the test fail by screwing the implementation. Why? Let’s look at small test example:

One of the killer features of Clojure is its ability to reload code and incrementally develop in a running environment. Another strength of Clojure/Clojure script is that it is deliberately a hosted language, leveraging the broader Java/Javascript ecosystem for libraries, frameworks, etc.

However, the dynamic code reloading and interacting with Java libraries can create some friction. Adding another layer of indirection sometimes reduces that friction. Let’s look at an example. Let’s assume we have a large Java library to which you provide a callback functions/object. Like an HTTP-server, network- or some other library. Easy, you implement the interface of the library. Note that the library instance is preserved with defonce.

This post is part of C# Advent Calendar 2020.

Update 6. December 2020: Some good small discussion on Reddit.com

It has been a while since I actively developed in C#. I mostly worked with C# and .NET during the 3.0 to 4.5 days and I did async/await work very early on, so I skip over that as well. After a job change, I didn’t touch C# for actual work. I mostly just watched the development from the sidelines via news. Today, I take a short look at some features. I will skip a lot and just add some of my highlights tour.

That the 127.0.0.1 IP is a loopback/localhost is widely known. It is used daily by many developers for testing of programs talking over the network. However, did you know that the whole 127.0.0.0/8 IP range are loopback addresses? You have a few million IP addresses reserved on each machine to talk to itself.

Time is complicated, really complicated. We have historically grown calendar systems, historical units, timezones, limelight savings times, etc. On top of that, we have precise atomic clocks and astronomical time definitions drifting apart and need periodical corrections, like with leap seconds.